Thats a very detailed explanation, THANKS!
have a couple questions though:
if the primary reason I'm using the steralizer is to kill algae spores so my
tank stays clean is it smart to only have the steralizer running for X hours
a day? Cant the spores be released and land and settle on the glass and
leaves during the off period? My second question is how much life of the
bulb is saved when you run it for 8 hours a day? I know that the turning on
of the bulb takes away from bulb life, but would the fact that its only run
for 1/3 of the time save bulb life in the long term? I am concerned since
36W PC florescents are $50 (not exactly cheap)

"Bruce Geist" wrote in message
...

Actually, the 9.2 factor will give you 99.99 % throughput through the
sterilizer. To get 99.9% throughput, the factor is 6.9.
See http://www.wideopenwest.com/~brucege...ver/index.html
for details.

One strategy is to set the flow rate through the sterilizer so that one
pass
kills target organisms you wish to kill. If you set the flow rate slow
enough that everything you want to kill is killed, then run your
sterilizer
long enough to "turnover" the tank water once or twice a day,
and then shut the sterilizer off.

Basically, the more slowly you put water through the sterilizer, the more
UV
exposure every bit of water passing through the sterilizer receives.
If
you have a 36 watt sterilizer with about a 3 inch diameter chamber for the
water, and your flow rate is about 100 gallons per hour, then you are
probably irradiating your water at about a 100 microwatt-seconds dose,
which
is
enough to kill most bacteria, algae, and many protozoa. (This is only a
crude estimate; I am working on developing some assessment tools on my
website which will provide more specific advice..) If you are using a
lower
wattage sterilizer, or a lower diameter sterilizer, then your flow rate
will
need to be lower still to achieve the same dose.

In the article I wrote cited above, I show that when you have run 99.9% of
the water through the sterilizer at least one time, in actuality 99.2% of
water has passed through 2 or more times, and 96.8% will have passed
through
the sterilizer 3 or more times! I recommend 6.9*(tank size in
gallons)/(flow rate in gallons) to be your target turnover time. If your
flow rate is chosen with some care, you need not run your sterilizer all
the time. You will save bulb life by running your sterilizer through only
one or two
turn-over intervals per day.

I hope you enjoy the article on turnover time; this is the first time I
have
published the web address. Remember that you can skip to the conclusion
and get the formula to use. I am in process of collecting data for a
suite
of articles on the topic UV sterilizers. Be watching this news group or
my
web site; I am waiting on data from a manufacturer. -Bruce Geist

"Christopher" wrote in message
rthlink.net...
is it wise to run the UV steralizer 24 hours a day? assuming that you
only
desire a 99.9% steralization rate you don't have to run the steralizer
that
much (depending upon gph through the steralizer and tank size). I've
read:

9.2 * (tank size / gph through steralizer) = hours a day UV steralizer
must
be on to attain 99.9% steralization rate (assuming uniform mixing).
This
said my calculation is at most 7 hours a day, should I just run it for 8
hours a day and save my bulb life and power bill?

Should I run it 24 hours a day to achieve 99.999% steralization or for 8
hours a day?